The present invention relates to a process for preparing certain coordination complexes of Group 4 metals in the +2 formal oxidation state starting from hydrocarbyloxide compounds wherein the metal is in the +3 or +4 formal oxidation state. The metal complexes are highly useful as components of addition polymerization catalysts used to prepare polyolefins.
In WO 95-00526 the preparation of certain titanium and zirconium complexes comprising a single, cyclic, delocalized -bonded ligand group wherein the metal of said complexes is in the +2 formal oxidation state from the corresponding metal halides is disclosed.
The above mentioned synthetic method to prepare the metal coordination complexes use metal halide compounds as starting materials, which are corrosive, toxic, and air and moisture sensitive. In order to facilitate handling thereof, the halide compound is typically converted to its ether-adduct in a separate step with for example THF or diethyl ether. This adduct formation step often proceeds with difficulty, requiring reduced temperatures and an inert atmosphere. For this and other reasons, the resulting yield of the aforementioned preparation is undesirably low.